1. Field of the Invention
In general, the present invention relates to string trimmers and the rotating heads of string trimmers. More particularly, the present invention relates to the mechanisms contained within string trimmer heads for winding, holding and dispensing new lengths of trimmer line when needed.
2. Prior Art Description
String trimmer machines have been commercially sold for over a quarter of a century. In this period of time, there have been many variations to the design of the string trimmer machine and especially to the trimmer head.
The trimmer head is the part of the string trimmer machine that rotates. The trimmer head holds lengths of trimmer line that rotate with the trimmer head. The rotating trimmer line contacts and cuts vegetation as it spins.
Depending upon the make, model, and manufacturer of the string trimmer machine, the trimmer head rotates either clockwise or counterclockwise during operation. The mix in the current retail market is generally an even split between clockwise and counterclockwise rotating string trimmer machines.
There are many types of trimmer heads on the market. The most common type of trimmer head is the bump-feed trimmer head. A bump-feed trimmer head contains an internal spool that holds a reserve of wound trimmer line. As the trimmer line wears away, it can be replaced from the internal spool. In a bump-feed trimmer head, a short length of line is released from the spool when the bottom of the trimmer head is impacted or “bumped” against a hard surface. Bump-activated trimmer heads are exemplified by U.S. Pat. No. 5,881,464 to Collins, entitled Line Head For Flexible Line Trimmer.
Many problems exist with traditional trimmer head designs. Primary among these problems concern the twisting of the string on the spool. Most trimmer heads contain two separate lengths of trimmer line. A trimmer head relies upon centrifugal force to pull the trimmer lines from the spool. If the trimmer lines tangle, twist or become buried under subsequent windings, the trimmer lines will not dispense in the proper manner. The trimmer head must then be disassembled, the trimmer string unwound and again rewound in the proper manner before the trimmer head will again work as designed. Furthermore, whenever the trimmer string supply is exhausted, the trimmer head must be manually disassembled. The spool is removed and rewound with a new supply of trimmer line. The spool is then reassembled back into the trimmer head. This process is difficult, labor intensive and highly time consuming. Furthermore, the entire process is often too difficult for many homeowners to complete successfully or even attempt.
Designs that attempt to overcome these problems have been proposed in the prior art. Such prior art is exemplified by U.S. Pat. No. 5,345,683 to Kanou, entitled, Rotary Cutter For Mowing Machine; U.S. Pat. No. 5,671,536 to Everts, entitled Line Feed Configuration For Line Trimmers; U.S. Pat. No. 6,263,580 to Stark, entitled Cutterhead For A Portable Handheld Brushcutter; U.S. Patent Application Publication No. 2004/0134078 to Pfalltzgraff, entitled Vegetation Cutter Device; and 2005/0076515 to Prouls, entitled, Trimmer Head For Use In Flexible Line Rotary.
U.S. Pat. No. 5,345,683 to Kanou discloses spool reloading solutions for bump and feed trimmers wherein trimmer line can be wound onto the internal spool without removing the spool from the trimmer head housing. However, the system taught by the Kanou patent requires additional user participation to anchor the trimmer line to the spool prior to winding/loading it onto the spool. Furthermore, the trimmer line spools are highly complex configurations which result in high cost manufacturing.
U.S. Pat. No. 5,765,287 to Griffini, entitled Cutting Head For Nylon-Cord Type Mowers describes a trimmer head that enables winding of a desired quantity of trimmer line onto a spool without removing the spool from the trimmer housing. In one embodiment, the device incorporates a rigid trimmer line guide tube that spans most of the diameter of the spool. Trimmer line is threaded into one trimmer line exit port in the trimmer head housing and passes through the guide tube. Upon exiting the guide tube, the trimmer line is passed through the opposite trimmer head housing exit port. When the desired length of trimmer line is threaded through the trimmer head, the installer rotates a knob integrally connected to the spool and the trimmer line is wound onto the core of the spool.
The trimmer head disclosed in the Griffini patent has certain disadvantages. The rigid trimmer line guide tube presents an obstruction in the spool chamber that hinders uniform and compact winding of the trimmer line onto the spool. Additionally, the trimmer line can also be damaged or severed as it comes into contact with the slotted edges at the opposite ends of the guide tube during winding. Furthermore, the Griffini patent, like all the prior art patents cited above, permit winding of trimmer line onto the trimmer line spool in only one direction, be it clockwise or counterclockwise, thereby limiting their practical application to a subset of the total population of powered vegetation trimmer apparatii.
The cited trimmer heads are designed to rotate in only a single direction. Accordingly, a trimmer head designed for a clockwise trimmer will not work on a counterclockwise trimmer. Furthermore, the parts from a clockwise trimmer head cannot be interchanged with any of the parts from a counterclockwise trimmer head. This requires a trimmer head manufacturer to create two sets of manufacturing tools, one for clockwise trimmer heads and one for counterclockwise trimmer heads. This significantly increases the cost associated with manufacturing trimmer heads.
U.S. Pat. No. 4,959,904 to Prouls, entitled Simple Flail Feedout Mechanism For A Rotary Mower, discloses a vegetation trimmer head that permits trimmer line to be wound onto the trimmer line spool in either a clockwise or a counterclockwise direction for appropriate clockwise or counterclockwise discharge. However, the user must engage in a cumbersome and time-consuming procedure when reloading trimmer line onto the spool. That is, a user must disassemble the trimmer housing, remove the spool, manually wind new line onto the spool, reinsert the spool into the housing, and finally reassemble the housing.
A need therefore exists for a string trimmer head that has an inexpensive yet reliable mechanism for dispensing trimmer line when needed. A need also exists for a string trimmer head that dispenses trimmer line without the trimmer line tangling, twisting, or binding. Furthermore, a need exists for a trimmer head that does not have to be disassembled to have new string added. Lastly, a need exists for a trimmer head that can be manufactured inexpensively and in a manner where many of the parts from a clockwise trimmer head are identical to parts in a counterclockwise trimmer head. These needs are met by the present invention as described and claimed below.